1. Field
The disclosed technology relates to a pixel and an organic light emitting diode (OLED) display device including the same, and in detail, relates to a pixel and an organic light emitting diode (OLED) display device including the same applying an inverse voltage if the organic light emitting diode (OLED) is not emitting light.
2. Description of the Related Technology
Various flat panel displays having reduced weight and volume when compared with a cathode ray tube have been developed. Flat panel displays include liquid crystal displays (LCD), field emission displays (FED), plasma display panels (PDP), organic light emitting diode (OLED) displays, and the like.
Among the flat panel displays, the organic light emitting diode display, which displays images by using an organic light emitting diode (OLED) that generates light by recombining electrons and holes, has a fast response speed, is driven with low power consumption, and has excellent emission efficiency, luminance, and viewing angle, such that it has recently been preferred.
Methods of driving an organic light emitting diode (OLED) display device generally include a passive matrix method and an active matrix method.
A passive matrix light emitting display device alternately has anodes and cathodes in the display area in a matrix, and pixels are formed at intersections of anode and cathode lines. In contrast, the active matrix light emitting display device has a thin film transistor for each pixel and each pixel is controlled by using the thin film transistor. A significant difference between the active matrix light emitting display device and the passive matrix light emitting display device is the difference of light emitting times of the organic light emitting device. The passive matrix light emitting display device substantially instantaneously emits light from the organic emission layer with high luminance, and the active matrix light emitting display device continuously emits light from the organic emission layer with low luminance.
In the active matrix light emitting display device, parasitic capacitance is low and power consumption is low compared with the passive matrix light emitting display device, however luminance is non-uniform. For this, a voltage programming method or a current programming method is used to compensate the characteristic of the driving transistor.
That is, each pixel of the organic light emitting diode (OLED) display device includes an organic light emitting diode (OLED), a driving transistor controlling a current to drive the organic light emitting diode (OLED), a switching transistor applying a data signal for expression of grayscales to the driving transistor, and a capacitor to store data voltages for the organic light emitting diode (OLED) according to desired timing by controlling the driving transistor. A voltage difference between the source and the gate of the driving transistor is stored in the capacitor, and then the driving transistor is connected to a voltage source to flow current as a video signal current in the driving transistor. Thus, the value of the current applied to the organic light emitting diode (OLED) is based on the video signal, and may be unrelated to the difference characteristic of the driving transistor such that the non-uniform luminance is improved.
However, in this method, the organic light emitting diode (OLED) is turned on/off by the switching of the driving transistor, and when the driving transistor is turned off, the anode of the organic light emitting diode (OLED) floats, and the life-span of the organic light emitting diode (OLED) is decreased. Also, undesired light emission of the organic light emitting diode (OLED) may be generated by a leakage current when the driving transistor is off such that the contrast ratio may be deteriorated. Accordingly, it is desired to develop a pixel in which the leakage current does not flow in the organic light emitting element when the driving transistor is off.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.